Training method of small-size NiTi alloy two-way shape memory effect

Abstract

The invention discloses a small-size NiTi alloy two-way shape memory effect training method which comprises the following steps: processing a NiTi alloy material into a thin strip shape, then performing solution treatment, and immediately performing water quenching; the NiTi alloy material treated in the first step is bent into a W shape at the normal temperature and installed in a constraint mold; the whole mold installed in the second step is placed in a heat treatment furnace to be subjected to aging treatment, after heat preservation is conducted for a certain time, the mold is cooled to the room temperature along with the furnace, a sample fixed to the aging treatment mold is unrestrained to be in a free state, and therefore the whole two-way shape memory effect training process is completed. The size of the W-like cross section at the room temperature is only 10 * 7 mm, the alloy can be applied to a miniature brake, and the two-way shape memory effect deformation rate of the obtained small-size NiTi alloy reaches up to 46.15%.

Description

Technical Field

[0001] The invention relates to the field related to shape memory alloys, and in particular to a training method for a two-way shape memory effect of a small-sized NiTi alloy and a product thereof. Background Art

[0002] NiTi shape memory alloy, a smart material, is widely used in aerospace, military, medical equipment and other fields due to its excellent superelasticity and shape memory effect. The shape memory effect of NiTi alloy is divided into three categories: one-way shape memory effect, two-way shape memory effect (TWSME) and full-way shape memory effect. The two-way shape memory effect of NiTi alloy refers to the phenomenon that the alloy can reciprocate between the high-temperature austenite phase shape and the low-temperature martensite phase shape as the temperature rises and falls without the assistance of external forces. With the development of the aerospace industry towards lightweight, high-strength and intelligent directions, the application of the two-way shape memory effect of NiTi alloy has received more and more attention.

[0003] The two-way shape memory effect is not an inherent property of NiTi alloys, and it can only be obtained after proper "training". At present, there are three ways to obtain the two-way shape memory effect: excessive deformation in the martensitic state, thermal-mechanical cycling, and constrained aging. The existing two-way memory effect training of NiTi alloy materials mostly adopts the constrained aging method, and the sample size is relatively large. For example, in CN114855008B, a semi-cylindrical constraint mold is used to train the two-way shape memory effect of high-nickel-rich nickel-titanium alloy, but the size of the alloy pattern is above 100×10mm, and the final two-way component changes in shape between bending and straightness. With the increasing application of NiTi alloys, the demand for the two-way shape memory effect of small-sized NiTi alloys is becoming more and more urgent. However, in the prior art, there is no corresponding small-sized NiTi alloy component with two-way shape memory effect. Therefore, it is urgent to develop a training method and product of the two-way shape memory effect of small-sized NiTi alloys. Summary of the invention

[0004] The purpose of the present invention is to provide a training method for the two-way shape memory effect of a small-sized NiTi alloy in view of the technical defects in the prior art. Another purpose of the present invention is to provide a corresponding small-sized NiTi alloy product.

[0005] The technical solution adopted to achieve the purpose of the present invention is:

[0006] A training method for a two-way shape memory effect of a small-sized NiTi alloy, the method comprising the following steps:

[0007] Step 1: Solution treatment

[0008] The NiTi alloy material is processed into a thin strip shape, and then subjected to a solid solution treatment, followed by immediate water quenching;

[0009] Step 2: Deformation of NiTi alloy

[0010] The NiTi alloy material processed in step 1 is bent into a W shape at room temperature and installed in a constraining mold;

[0011] Step 3: Aging treatment

[0012] The mold installed in step 2 is subjected to aging treatment as a whole, with an aging temperature of 300-500°C, kept warm for 100-300 minutes and then cooled to room temperature, and the sample fixed on the aging mold is released to a free state, thereby completing the overall two-way shape memory effect training process.

[0013] In the above technical solution, the NiTi alloy material in step 1 is Ni50Ti50.

[0014] In the above technical solution, the size of the thin strip in step 1 is (40-70)×(2-4)×(0.2-0.5) mm.

[0015] In the above technical solution, in step 2, the thin strip is bent at a fixed length, a total of 4-7 times, into a W-shape, preferably, into a W-shape with five arms.

[0016] In the above technical solution, the mold in step 2 is a hollow cuboid.

[0017] In the above technical solution, the outer contour of the mold is (12-20)×(9-16) mm, and the size of the hollow rectangle is 2.2-4.2 mm in width and 5.0-7.0 mm in length.

[0018] In the above technical solution, the aging treatment in step 3 is carried out in a heat treatment furnace.

[0019] In the above technical solution, the temperature of the solution treatment in step 1 is 700-1000°C and the time is 60-180 minutes.

[0020] Another aspect of the present invention also includes a small-sized NiTi alloy component prepared by the training method.

[0021] In the above technical solution, the small-sized NiTi alloy component has an opening size of 7-10 mm and a width of 7-12 mm at room temperature.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Realize small-size sample training: Two-way memory effect training mostly uses samples with a size of 100×10mm or more, and the changing shapes are mostly bending and straightening. The training method proposed in the present invention realizes the elongation and shortening of the W-shaped structure. The cross-sectional size of the W-shaped structure at room temperature is only 10×7mm. Compared with the prior art, the size of the component is greatly reduced and can be applied to micro brakes.

[0024] 2. Excellent two-way shape memory effect: The present invention can achieve a two-way shape memory effect with a deformation rate of up to 46.15%.

[0025] 3. The training method is simple and the training efficiency is high: a stable two-way shape memory effect can be obtained through constrained aging treatment, the heat treatment time is short, the mold structure is simple, and the two-way shape memory effect training can be carried out on small-sized NiTi components in batches and efficiently.

[0026] 4. by the training mode of the present invention, through the constraint aging treatment, a large amount of lens-shaped coherent Ni4Ti3 can be separated out in the NiTi alloy material, produce stronger coherent internal stress field, and there is a stress field in a certain direction in the constraint state at the same time, therefore, the coherent phase will be preferentially separated out and grown up under the effect of this internal stress field, namely, the coherent phase of a specific orientation is separated out along the constraint direction, thereby forming a stable coherent internal stress field of a specific orientation. In the cooling process, the martensitic variant in the favorable orientation preferentially nucleates and grows up under the effect of the stable coherent internal stress field, resulting in macroscopic shape change. In the temperature-raising process, the favorable orientation variant undergoes reverse martensitic transformation and returns to the austenite state, and macroscopic shape change occurs, and the coherent internal stress field is re-established at the same time. In this way, the NiTi alloy material shows good double-pass memory effect in the cold and hot cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is an overall process flow chart of the two-way shape memory effect training scheme of small-sized NiTi alloy according to the present invention;

[0028] Figure 2 Schematic diagram (a) and actual diagram (b) of a constraining mold according to the present invention;

[0029] Figure 3 A schematic diagram of a test position of a sample opening size according to the present invention;

[0030] Figure 4 The figures are based on multiple examples of the present invention, and are used to more specifically show the high and low temperature state dimensions and deformation of the small-sized NiTi alloy strip after training with different constraint mold sizes.

[0031] Figure 5It is a diagram of several examples according to the present invention, used to more specifically show the TWSEM deformation rate of a small-sized NiTi alloy strip after training with different constraint die sizes;

[0032] Figure 6 1 and 2 show the shapes of the small-sized NiTi alloy after constrained aging training according to the present invention in the heating (a) and cooling (b) states. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Example 1

[0035] A training method for a two-way shape memory effect of a small-sized NiTi alloy comprises the following steps:

[0036] First, the commercial cold-rolled Ni 50 Ti 50 The thin strip sample with the size of 50×2×0.2 (mm) was subjected to solution treatment at a temperature of 750℃ for 60 minutes, followed by water quenching. Next, the NiTi thin strip after the above treatment was bent once every 10mm at room temperature, and finally bent into a W-shape and installed in a constrained mold. The mold thickness is 11mm, and its schematic diagram and actual picture are as follows Figure 2 As shown, the outer contour is 12×9.2mm, the hollow rectangular size is 2.2mm wide and long ( Figure 2 The L in the mold is 5.0-7.0mm. Next, the mold is placed in a heat treatment furnace for aging treatment at a temperature of 300-500°C. After 150 minutes of heat preservation, the mold is cooled to room temperature. Finally, the sample fixed on the mold is released to a free state. In addition, a two-way shape memory effect evaluation can also be performed in this step.

[0037] According to a preferred embodiment of the present invention, the shape memory effect of NiTi alloy can be recorded by photographic method, which includes measuring the shape memory effect of NiTi alloy in a fully austenitic state at 70°C. Figure 3 The opening size shown is the opening size at room temperature (25°C). The deformation rate is the percentage of the change to the opening size in the fully austenite state, where the change is defined as the absolute value of the difference between the opening size in the fully austenite state and the fully martensite state.

[0038] Example 2

[0039] The same method as in the above-mentioned embodiment 1 was used to perform constrained aging treatment using a hollow mold with a size of 2.2×5.0 mm, and the aging temperature was 450°C. The small-sized NiTi component obtained according to the above steps was then placed on a 70°C heating plate (heating state) and in a room temperature environment (cooling state), and the opening size under each temperature environment was recorded to perform a two-way shape memory effect evaluation. The opening size was 5.5 mm at 70°C, and 7.8 mm at room temperature, with a variation range of 2.3 mm and a deformation rate of 41.82%.

[0040] Example 3

[0041] The same method as in the above-mentioned embodiment 1 was used to perform constrained aging treatment using a hollow mold of 2.2×5.5 mm, and the aging temperature was 450°C. The small-sized NiTi component obtained according to the above steps was then placed on a 70°C heating plate (heating state) and at room temperature (cooling state), and the opening size under each temperature environment was recorded to perform a two-way shape memory effect evaluation. The opening size was 6.5 mm at 70°C, and 9.5 mm at room temperature, with a variation range of 3 mm and a deformation rate of 46.15%. The actual picture is as follows: Figure 6 shown.

[0042] Example 4

[0043] The same method as in the above-mentioned embodiment 1 was used to perform constrained aging treatment using a hollow mold with a size of 2.2×6.0 mm, and the aging temperature was 450°C. The small-sized NiTi component obtained according to the above steps was then placed on a 70°C heating plate (heating state) and in a room temperature environment (cooling state), and the opening size under each temperature environment was recorded to perform a two-way shape memory effect evaluation. The opening size at 70°C was 7.0 mm, and the opening size at room temperature was 9.5 mm, with a variation range of 2.5 mm and a deformation rate of 35.71%.

[0044] Example 5

[0045] The same method as in the above-mentioned embodiment 1 was used to perform constrained aging treatment using a hollow mold with a size of 2.2×7.0 mm, and the aging temperature was 450°C. The small-sized NiTi component obtained according to the above steps was then placed on a 70°C heating plate (heating state) and in a room temperature environment (cooling state), and the opening size under each temperature environment was recorded to perform a two-way shape memory effect evaluation. The opening size was 8.0 mm at 70°C, and 10.0 mm at room temperature, with a variation range of 2.0 mm and a deformation rate of 25.00%.

[0046] Example 6

[0047] The same method as in the above-mentioned embodiment 1 was used to perform constrained aging treatment using a hollow mold of 2.2×5.5 mm, and the aging temperature was 350°C. The small-sized NiTi component obtained according to the above steps was then placed on a 70°C heating plate (heating state) and in a room temperature environment (cooling state), and the opening size under each temperature environment was recorded to perform a two-way shape memory effect evaluation. The opening size was 7.5 mm at 70°C, and 8.0 mm at room temperature, with a variation range of 0.5 mm and a deformation rate of 6.25%.

[0048] Example 7

[0049] The same method as the above embodiment is adopted, except that a mold with a hollow size of 2.2×5.5 mm is used for constrained aging treatment, and the aging temperature is 500°C. Then the small-sized NiTi component obtained according to the above steps is placed on a 70°C heating plate (heating state) and in a room temperature environment (cooling state), and the opening size under each temperature environment is recorded to perform a two-way shape memory effect evaluation. The opening size is 7.0 mm at 70°C, and the opening size is 7.0 mm at room temperature, with a variation range of 0.1 mm and a deformation rate of 0.1%.

[0050] Comparative Example 1

[0051] First, the commercial cold-rolled Ni 50 Ti 50 The thin strip sample processed into a size of 90×2×0.2 (mm) is solution treated, wherein the temperature of the solution treatment is 750°C and the time is 60 minutes, followed by immediate water quenching. Next, the sample is placed in a semicircular mold (refer to the device shown in CN114855008B). Again, the installed mold is placed in a heat treatment furnace as a whole and an aging treatment is performed, wherein the aging temperature is 450°C, and after keeping warm for 150 minutes, it is cooled to room temperature with the furnace. Finally, the sample fixed on the mold that has completed the above treatment is released from the constraints to a free state. In addition, a two-way shape memory effect evaluation can also be performed in this step.

[0052] The shape memory effect of NiTi alloy was recorded by photography, including the measurement of the sample in the fully austenitic state at 70°C, which was a complete arc shape. The sample was straight in the fully martensitic state at room temperature. Therefore, the sample can only be bent and straightened, and the final product is 90 mm long at room temperature, that is, large in size.

[0053] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A training method for the two-way shape memory effect of a small-sized NiTi alloy, characterized in that: The method comprises the following steps: Step 1: Solution treatment The NiTi alloy material is processed into a thin strip shape, and then subjected to a solid solution treatment, followed by immediate water quenching; Step 2: Deformation of NiTi alloy The NiTi alloy material processed in step 1 is bent into a W shape at room temperature and installed in a constraining mold; Step 3: Aging treatment The mold installed in step 2 is subjected to aging treatment as a whole, with an aging temperature of 300-500°C, kept warm for 100-300 minutes and then cooled to room temperature, and the sample fixed on the aging mold is released to a free state, thereby completing the overall two-way shape memory effect training process.

2. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 1, characterized in that: The NiTi alloy material described in step 1 is Ni 50 Ti 50 .

3. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 1, characterized in that: The size of the thin strip in step 1 is (40-70)×(2-4)×(0.2-0.5) mm.

4. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 3, characterized in that: In step 2, the thin strip is bent at a fixed length for 4-7 times in total, and is bent into a W-shape. Preferably, it is bent into a W-shape with five arms.

5. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 1, characterized in that: The mold in step 2 is a hollow cuboid.

6. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 5, characterized in that: The outer contour of the mold is (12-20)×(9-16) mm, and the size of the hollow rectangle is 2.2-4.2 mm in width and 5.0-7.0 mm in length.

7. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 1, characterized in that: In step 3, the aging treatment is carried out in a heat treatment furnace.

8. A training method for the two-way shape memory effect of a small-sized NiTi alloy as claimed in claim 1, characterized in that: The temperature of the solution treatment in step 1 is 700-1000° C. and the time is 60-180 min.

9. A small-sized NiTi alloy component obtained by the training method according to any one of claims 1 to 8.

10. A small-sized NiTi alloy component according to claim 9, characterized in that: The small-sized NiTi alloy component has an opening size of 7-10 mm and a width of 7-12 mm at room temperature.

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